Over the years, the design of concrete structures has evolved and vastly improved. Various mechanisms for reinforcing concrete structures have been tested and implemented to augment the concrete tensile strength. As known in the art, reinforced concrete reaches its highest potential when it is used in a prestress or post-tensioned fashion. In prestressing, reinforcing tendons of high tensile strength wires or similar materials are stretched to a certain predetermined limit and then high-strength concrete is placed around them. When the concrete is set, it holds the steel in tight grip, preventing slippage or sagging. Post-tensioning follows a similar principle but the reinforcing tendons are held loosely in place while the concrete is placed around them. After the concrete cures, the reinforcing tendons are stretched by hydraulic jacks and securely anchored into place. Prestressing is done with individual members in the shop while post-tensioning is part of the structure on the site.
FIG. 1 illustrates various components of a typical post-tension assembly designated generally at 10. System 10 includes a tendon 12 having an exposed end 13 protruding from a sheath 14. End 13 of tendon 12 is typically fitted through an extension tube 16. Extension tube 16 has a diameter slightly larger than sheath 14 such that one end 16a of tube 16 may overlie sheath 14. The opposite end 16b of tube 16 fits over, and communicates with, a rear tubular portion 18 of an anchor 20. Rear tubular member 18 includes an aperture (not shown) which communicates with a frontal aperture 22. Frontal aperture 22 defines a cavity in which wedges 24 and 26 are disposed, as shown in FIG. 2, below.
FIG. 2 illustrates an assembled view (in one-fourth cutaway perspective) of system 10 shown in FIG. 1. As known in the art, tendon 12 is disposed through extension tube 16 and through anchor 20. In one known embodiment, end 16b of extension tube 16 is force-fitted over rear tubular member 18. The other end 16a of extension tube 16 is sealed to sheath 14, by use of tape or other means.
After tendon 18 extends through frontal aperture 22 (see FIG. 1), and assuming the far end of the tendon (not shown) is fixed in place, tension is applied to tendon 16, typically by use of a hydraulic jack. While applying this tension, wedges 24 and 26 are forced in place on both sides of tendon 12 within the wedge cavity defined by aperture 22. Once in place, teeth 24a and 26a of wedges 24 and 26 operate to lock tendon 12 in a fixed position with respect to anchor 20. Thereafter, the tension supplied by the hydraulic device is released and the excess tendon extending outward from anchor 20 is cut by a torch or other known device. Wedges 24 and 26 thereafter prevent tendon 12 from releasing its tension and retracting inward with respect to anchor 20. Moreover, this tension provides additional tensile strength across the concrete structure.
As known in the art, metallic components within concrete structures may become exposed to many corrosive elements, such as de-icing chemicals, brackish water, and salt water. If this occurs, and the exposed portions of the anchor suffer corrosion, the anchor and/or its related parts may weaken. The most sensitive area responsive to these corrosive effects is the wedge cavity defined by aperture 22. Particularly, teeth 24a and 26a of wedges 24 and 26 are fairly delicate, yet of paramount importance in retaining the tendon under stress. Consequently, once the teeth deteriorate, the gripping effect of the wedges is diminished or eliminated and, hence, the tendon either partially or completely slips from the grasp of the anchor. This slippage may cause loss of the tension effects across the structure.
Various attempts have been made in the prior art to reduce or eliminate the potential for corrosion within the wedge cavity of the anchor. For example, U.S. Pat. No. 5,024,032, entitled "Post-Tensioning Anchor" and issued to Rodriguez on Jun. 18, 1991, discloses a post-tension anchor and cap. The cap friction fits with the anchor in an effort to enclose the wedge cavity from external materials. The friction-fitting cap includes tabs or so-called "ears" around which securing filaments are tied. The securing filaments are purported to retain the cap within a press-fit engagement of the anchor, thereby precluding corrosives or contaminants from reaching the wedge cavity of the anchor.
U.S. Pat. No. 4,918,887, entitled "Protective Tendon Tensioning Anchor Assembly" and issued to Davis et al. on Apr. 24, 1990, discloses the combination of an anchor plate, a sealing cap and a resilient sealing ring. The combination is used in an effort to seal the wedge assembly of the anchor from the external environment. The combination represents a relatively complicated configuration for a sealing cap wherein various locking fingers and a specially Shaped sealing ring are necessary in an effort to seal the wedge cavity of the anchor from external contaminants.
As yet another example, U.S. Pat. No. 4,773,198, entitled "Post-Tensioning Anchorages for Aggressive Environments", and issued to Reinhardt on Sep. 27, 1988, discloses an alternative anchor and sealing cap assembly. The sealing cap is provided with threads for threading into a lip of the anchor plate for fluid sealing. Alternative seals such as "snap rings, bayonet fittings or other" fittings are also discussed.
As yet a final example, U.S. Pat. No. 4,719,658, entitled "Hermetically Sealed Anchor Construction For Use In Post Tensioning Tendons", and issued to Kriofske on Jan. 19, 1988, discloses an anchor and "plug" for fitting to the anchor. The plug includes a grease fitting through which grease may be injected, thereby forcing it into the cavities surrounding the anchor.
Each of the prior,art references discussed above, as well as others known in the art, all purport to attempt to maintain the wedge Cavity of the anchor free of contaminants. Unfortunately, however, each of the efforts of the prior art have reflected various drawbacks. For example, many of the devices are highly complicated to manufacture and/or use. This increased complication significantly increases costs which, when spread over hundreds or thousands of devices, may significantly affect the total price for constructing the concrete structure. Moreover, the more sophisticated devices require greater skill and time expenditure during installation. Consequently, not only are costs of the device increased, but so are the risks of wrongful or erroneous use of the device. If the device is not properly implemented, the device may fail to achieve its intended objective.
It is therefore an object of the present invention to provide an improved method and sealing apparatus for use with an anchor assembly.
It is a further object of the present invention to provide such an apparatus and method for reducing the costs of manufacturing and installing the overall assembly.
It is yet another object of the present invention to provide such an apparatus and method such that the amount of steps necessary in constructing and installing the device are simplified and/or reduced.
It is further object of the present invention to provide such a method and apparatus such that the number of component parts are reduced.
Still other objects and advantages of the present invention will become apparent to those of ordinary skill in the art having reference to the following specification, together with its drawings.